# std::tuple_element<std::ranges::subrange>

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< cpp‎ | ranges‎ | subrange

Defined in header `<ranges>` |  |
template< class I, class S, ranges::subrange_kind K > struct tuple_element<0, ranges::subrange<I, S, K>>; | (1) | (since C++20)
template< class I, class S, ranges::subrange_kind K > struct tuple_element<0, const ranges::subrange<I, S, K>>; | (2) | (since C++20)
template< class I, class S, ranges::subrange_kind K > struct tuple_element<1, ranges::subrange<I, S, K>>; | (3) | (since C++20)
template< class I, class S, ranges::subrange_kind K > struct tuple_element<1, const ranges::subrange<I, S, K>>; | (4) | (since C++20)

The partial specializations of `std::tuple_element` for std::ranges::subrange provide compile-time access to the iterator or sentinel type of a `subrange`, using tuple-like syntax. They are provided for structured binding support.

1,2) Obtains the iterator type, i.e. `I`.
3,4) Obtains the sentinel type, i.e. `S`.

### Member types

Member type | Definition
`type` | (1,2) `I` (3,4) `S`

### Notes

As `get` functions for `subrange` return iterators and sentinels by value, const qualifier is not added to the result types when the `subrange` is const-qualified (but not volatile-qualified).

If the `subrange` is volatile-qualified, the result types are also volatile-qualified because the partial specialization for volatile or const volatile types are used. Such usage is deprecated.

### Example

Run this code

    #include <iterator>
    #include <list>
    #include <ranges>
    #include <type_traits>

    int main()
    {
        std::list<int> list{3, 1, 4, 1, 5, 9, 2, 6};

        std::ranges::subrange subrange
        {
            std::counted_iterator{std::begin(list), 4},
            std::default_sentinel
        };

        static_assert(
            std::is_same_v<
                std::tuple_element_t<0, decltype(subrange)>,
                // implementation-defined type:
                std::counted_iterator<std::_List_iterator<int>>
                >);

        static_assert(
            std::is_same_v<
                std::tuple_element_t<1, decltype(subrange)>,
                std::default_sentinel_t
                >);
    }

### See also

Structured binding (C++17) | binds the specified names to sub-objects or tuple elements of the initializer
tuple_element (C++11) | obtains the element types of a tuple-like type (class template)
std::tuple_size<std::ranges::subrange> (C++20) | obtains the size of a std::ranges::subrange (class template specialization)

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